WARNING: This article contains views that some readers will object to on public health grounds. It should/should not* be banned. (* Delete as appropriate). Dr John Gray, political philosopher and libertarian likes to think of himself as ''a liberal, but a liberal who likes to be consistent''. The description is ample demonstration of the danger of the over-use of political labels, but little help in defining his views. For the British academic is only a liberal in the 19th century sense of free-thinker and free-trader. Otherwise his ideas sit better with the neo-conservatism of the 1980s. Certainly, no one among what he calls the progressive liberals would regard his opinions as ''politically correct''. The crux of his argument is that freedom of expression should apply to advertisers no less than to artists, writers, politicians and religious groups. Unrestricted advertising is the guarantee of a free media. Without it newspapers would be expensive and their circulation restricted to the point where their viability was threatened. Yet it takes a back seat to other freedoms. ''My concern is that in different parts of the world, commercial freedom of expression is being unjustly downgraded in importance compared with other forms,'' he says, taking a swipe at the growing international trend to ban or restrict certain types of advertising to protect public health or save the consumer from his own folly. Why prohibit tobacco advertisements, out of what Dr Gray sees as misplaced paternalism, while forms of artistic expression which coarsen the sensibilities and undermine morality - Madonna's book Sex for instance - cannot be touched? ''If people are so incompetent to assess advertisements that we have to curb them, why should they be more competent to choose their own rulers?'' asks Dr Gray, who is in town for the International Advertising Association's symposium on Advertising andthe Media in a Free Market Economy. Tobacco is the obvious target. But the European Community for instance is working on proposals covering commercials for alcohol, financial services and, claims Dr Gray, even advertisements for children's toys. Let's concentrate on tobacco. We are on dangerous ground here, but Dr Gray, who says he is not sponsored by anyone, ploughs on regardless. There is empirical evidence, he claims, that advertising does not increase the aggregate of tobacco smoked, merely the market share of particular brands. The tobacco industry must love him. ''That's for them,'' he says, unruffled. The danger of banning advertising - for a product which everyone proposes should remain legal - is that it freezes particular patterns of consumption while the debate on scientific evidence is still going on. There is also empirical evidence, Dr Gray, (which any smoker and anyone who has ever tried giving up smoking can tell you about, because it rests on personal experience), that seeing someone light up in public or on television arouses a terrible urge to follow suit. Logically, that increases consumption. A non-smoker, he seems taken aback by this argument. ''I suppose that could be true of any addiction,'' he wonders aloud. His position remains. As further evidence of rampant paternalism, he turns to the subject of vitamins, a personal hobby-horse about which he is less vulnerable than tobacco. The European Community, he says, is working on plans to class any vitamin product containing more than the American recommended daily dose as medicine, which would affect its availability, cost to the consumer and the manner in which it may be advertised. ''Many people who see themselves as liberals would find it an extraordinary restriction of individual freedom. ''It's an infringement on the right to look after one's own health,'' he says whipping out a box of pills. ''That reminds me,'' he adds, smiling.